(1) Field of the Invention
This invention relates to a substrate cleaning and drying apparatus for cleaning and then drying semiconductor wafers, glass substrates for photomasks, glass substrate for liquid crystal displays, substrates for optical disks or the like (hereinafter called simply substrates). More particularly, the invention relates to a technique for performing drying treatment by suction from a holding device, after cleaning treatment.
(2) Description of the Related Art
Conventionally, this type of apparatus withdraws substrates cleaned in a treating tank up from deionized water stored in the tank, and moves the substrates to a drying device separate from the treating tank. Thereafter, the substrates are dried by air flowing down in a cleanroom while the air is sucked from substrate holders supporting the substrates (see Japanese patent No. 3244220, paragraph No. 0015 and FIG. 3, for example).
The above apparatus is satisfactory for drying hydrophilic substrates having smooth surfaces, such as substrates having oxide film formed thereon or substrates with oxide film, after cleaning treatment with an oxidizer such as a hydrogen peroxide solution.
While the above patent does not give a detailed description regarding the shape of suction bores in the substrate holders, it is understood that a single round bore is formed in each substrate holder as a suction bore. In the light of the level of requirement by semiconductor device makers to date, certain stains (i.e. residues called water marks) are regarded as presenting no serious problem.
The conventional apparatus having such a construction has the following drawbacks:
(1) In a semiconductor device manufacturing process, devices are made from substrates having a complicated three-dimensional configuration. Specifically, the substrates have holes such as contact holes and via holes, groove-like trenches, fins like walls standing close together, and so on. Their surface conditions are diverse from hydrophilic to hydrophobic surfaces. In drying treatment following cleaning of the substrates performed in the course of such device manufacture, the substrates are dried with air taken into a cleanroom as noted above. This drying operation is time-consuming. Deionized water retained by the hydrophilic surfaces could cover the hydrophobic surfaces. Silicon, for example, could dissolve into deionized water remaining on the hydrophobic surfaces. In the gas-liquid-solid interfaces, silicon could be oxidized by the oxygen in the atmosphere.
Further, as the oxidized silicon dissolves into the deionized water, the oxidized silicon and other silicon accumulate in the deionized water. When dried, hydrates of the oxidized silicon, i.e. water marks, are formed to deposit on silicon surfaces. This gives rise to a problem of deteriorating the characteristics of the devices.
Particularly, in cleaning before forming gate oxide film, and cleaning before gate insulation film deposition (CVD), these hydrates of oxidized silicon are electrically insulators and act as resistors. Thus, a normal ohmic contact cannot be obtained, and the structure of the deposited CVD film is distorted by the water marks. This results in defective device characteristics or malfunctioning of the devices per se.
(2) With the recent trend toward larger substrates, a substrate cleaning apparatus, unless designed compact, will pose a serious problem of occupying a large area in a cleanroom. A development has been in progress from a huge apparatus construction in which substrates are linearly moved from one side toward the other side, to a compact apparatus construction having a substrate transport system and an interface only at one side. Where the conventional apparatus noted hereinbefore were employed in combination with such an apparatus, substrates would be transported above the apparatus. Substrate could not be transported during drying treatment of other substrates. Thus, it is practically impossible to employ the conventional apparatus. Even if it were employed, the apparatus, because of low throughput, would fail to demonstrate a satisfactory performance.
Device makers have begun to point out that, with further progress in the technique of semiconductor devices, even minute stains on substrate edges will present a problem in device manufacture. Such stains, for example, accumulate on the substrate transport system, contaminate other substrates, detach from the substrates contaminated in the cleaning apparatus or the like into the cleaning solution or rinse solution to adhere to device surfaces, and ultimately cause device defects.
Each substrate holder in the conventional apparatus defines only one ordinary round bore. Such a construction cannot meet the above requirement.
The above problem arises from a physical positional relationship between the round bore and the substrate holder. That is, a gas flowing into the round bore from right above dries, in a relatively short time, deionized water adhering to a lower edge of the substrate lying over the round bore. However, the drying gas does not flow, in sufficient quantities, down opposite portions outward of the above lower edge, more particularly, arcuate portions obliquely downward from the center of the substrate and portions adjacent positions pinched by the round bore of the substrate holder. Such portions are slow to dry, and stains are formed thereon. These stains, in the case of a silicon substrate, are silicon and oxidized silicon remaining as hydrates of oxidized silicon on substrate surfaces after drying treatment. Silicon dissolves into remaining deionized water, and oxidized silicon is formed in gas-liquid-solid interfaces and dissolves into the remaining deionized water, both accumulating on the substrate surfaces.